Viagra (sildenafil) tablets to treat erectile dysfunction available in 25mg, 50mg, and 100mg strengths. Stretching. Stretching involves attaching a stretcher or extender device to the penis to exert traction. A few small studies have reported length increases of half an inch to almost an inch (about 1 to 2 centimeters) with these devices. However, the studies are not high quality. More rigorous re